Overvoltage protection network

ABSTRACT

Voltage regulation is provided by a single voltage regulator to a number of individual circuits. Each of the individual circuits is independently controlled by a switch in series with the voltage regulator across a voltage supply. The switches consist of switching diodes which individually become conductive when the applied voltage across the particular circuit undergoes an excursion above a certain level. The voltage regulator may consist of a zener diode. When an individual switching diode conducts, the voltage determined by the zener diode is applied to the corresponding circuit to establish a regulated voltage across a respective load circuit.

Acevedo [451 Aug. 1,1972

[54] OVERVOLTAGE PROTECTION NETWORK [72] Inventor: Generoso Acevedo, Milan, Tenn.

[73] Assignee: International Telephone and Telegraph Corporation, New York, NY.

COUNTER Primary Examiner-James D. Trammell Attorney-C. Cornell Remsen, Jr. et a1.

[57] ABSTRACT Voltage regulation is provided by a single voltage regulator to a number of individual circuits. Each of the individual circuits is independently controlled by a switch in series with the voltage regulator across a voltage supply. The switches consist of switching diodes which individually become conductive when the applied voltage across the particular circuit undergoes an excursion above a certain level. The voltage regulator may consist of a zener diode. When an individual switching diode conducts, the voltage determined by the zener diode is applied to the corresponding circuit to establish a regulated voltage across a respective load circuit.

I 6 Claims, 1 Drawing Figure P'ATENTEDAus 1 m2 COUNTER DI D2 D3 V2 J I N VEN TOR. GENEROSO ACEVEDO BACKGROUND OF THE INVENTION 1 Field of the Invention The present invention relates to the regulation of voltages and especially to the prevention of the appearance of excessively high voltages across each of a plurality of voltage sensitive circuits. It has particular application to situations in which it is necessary to apply a voltage, for test or metering purposes, which may exceed safe levels of particular elements in those circuits. Protection may be extended by application of the invention to any circuits or devices employing electrical energy. It has particular application to the protection of electric indicator lamps in telephone switching circuits but may be used in other circuits to protect meters, electronic components, electro-luminescent devices, relays and the like.

2. Description of the Prior Art Zener diodes have been used extensively as overvoltage protection devices. Characteristically, they have been used in one of two ways, or modes. In one mode, a single zener diode has been used in a common circuit, such as a power supply circuit, to regulate the voltage across two or more individual components. In the other mode, a separate zener diode has been provided for each component to be protected.

When a zener diode is used in a common circuit involving a number of components be be protected, i.e., in the first mode, the power rating of the zener must be relatively high. By way of example, even in a power supply having a low current rating, a requirement for to 50 watts is common.

When a number of zener diodes are used as protection across individual circuits in the second mode referred to above, the power ratings for each of the zener diodes is reduced. However, the number of zener diodes increases in direct proportion to the number of circuits to be protected.

SUMMARY OF THE INVENTION The present invention has as a primary object to overcome the disadvantages of the prior art and to enable the use of a single medium power zener diode, or other single voltage regulator, to protect a number of individual components in separate circuits. In a particular embodiment, switches in the form of low cost switching diodes are used to interconnect the zener diode and each of the circuits needing voltage regulation. The zener diode is required to dissipate power only to those circuits which are connected to it by this switching action. Energy consumption through the zener diode depends on the power demand that obtains in the particular system at various times and the probability of a particular maximum may be used in determining the size of zener that is required.

BRIEF DESCRIPTION OF THE DRAWING The above mentioned and other features and objects of this invention and the manner of obtaining them will become more apparent, and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawinG, in which the sole Figure is a schematic wiring diagram depicting an embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the Figure an embodiment of the invention is shown for providing protection to a number of electric lamps L1, L2, L3 and L4. The lamps in a particular case function as indicators of whether the respective leads S1, S2 and S3 are grounded by closure of contacts s1, s2, and/or s3, or not. In a telephone switching system, for example, theleads S1, S2 and S3 may be sleeve leads, the contacts :1, s2, and s3 are controlled by the external switching system, and the lamps L1, L2 and L3 may be busy indicators which are lit to indicate a grounded, and therefore busy, condition of the respective sleeve. Lamps L3 and L4 are shown connected in parallel so that they can display the status of lead S3 at two locations. Resistors R1, R2, and R3 are selected in accordance with calculations including consideration of the negative voltage (typically 48 volts) at terminals 7, 8, and 9 to assure that the voltage V3 is correct for the lamps. In a typical case, resistor R3 has one-half the resistance of R1 when the lamps are all of the same type.

Tests of various kinds may be applied to the sleeve 5 leads in telephone switching systems while the sleeve leads are registering busy. Among these are metering and identification tests which involve the application of positive potentials to the grounded sleeves. By way of example, in a PABX in use in a hotel or a motel it may be necessary to count the number of calls made by the guests. For this purpose, simple electro-mechanical counters may be employed which respond by a count of one when they are pulsed following completion of a calling connection.

In a PABX of the kind discussed above an embodiment of the present invention is used in order to get a meter reading indicating a call has been completed. For this purpose a previously closed relay contact s1, s2, or $3 is opened by central control equipment and the potential (+48 from the test unit is applied at the same time. Ground potential is maintained on the sleeve during this period through an electromechanical counter or meter at 14. The potential supplied from the test unit 12 is a positive going pulse which is applied momentarily to operate the counter at 14. The counter in a particular circuit requires a positive potential of 48 volts to operate properly and the bias at a terminal 7, 8, or 9 is a negative 48 volts, so that in the absence of protective devices the voltage applied from the test unit to the sleeve will effectively double the potential across the lamps L1, L2 or L3, causing the lamps to glow brightly and frequently to burn out. In order to enable the system to supply the +48 volts needed to operate the meter 14 and at the same time protect the busy lamps, the circuit represented by one of the resistors R1, R2 or R3 and the corresponding diode circuit D1-Zl, D2-Zl, or D3-Z1 has been supplied. The diode circuits, as is explained more fully in the paragraphs following this one, limit the voltage levels at terminals l, 2 and 3. The resistors R1, R2 and R3 provide a voltage drop enabling the +48 volts to be applied from the test unit 12 to the meter while, at the same time, the voltage at terminal 1, 2, or 3 is limited to a value nearer the ground potential by operation of the corresponding diode circuits.

As previously mentioned, in the absence of protective elements, the application of positive pulses from the test unit 12 to a terminal such as l, 2, or 3 will increase the potential across a corresponding lamp L1, L2 or L3 causing it to glow brightly and perhaps burn out. In a specific instance, with a negative potential of 48 volts at a terminal 7 the addition of a positive potential of 48 volts at a terminal 1, from the test unit 12, will cause the current flow in the lamp L1 to double. It has been indicated previously that a purpose of this invention is to prevent such voltage overloads.

Switches in a preferred embodiment of this invention include diodes D1, D2, and D3 which are selected from low cost switching diodes. The voltage regulator incorporates a zener diode Z-l selected, typically, although not necessarily, to operate with an avalanche voltage of the same magnitude as V3. In a particular example, the bias voltage at terminal was selected to be 4.8 volts.

Under normal operating conditions, V3 is greater than V1 plus V2 when corresponding sleeves are grounded through s1, s2, or s3 and no current flows through the diodes D1, D2, D3, or Z1. Assuming that a positive voltage appears on sleeve lead 81 in association with a test of the sleeve, or by accident, the drop V3 across Ll tends to rise. When the voltage at terminal 1 becomes sufficiently more positive so that diode D1 will conduct and the zener Zl will avalanche, the voltage V3 will be stabilized to equal V1 V2. Similarly, with Zl conductive, if a positive voltage above a particular magnitude appears at terminal 3, the diode D3 will conduct, and the zener diode Z1 will provide a regulated voltage across L3 and L4 equal to V3.

While the principles of the invention have been described above in connection with specific apparatus and applications, it is to be understood that this description is made only by way of example and not as a limitation on the scope of the invention.

lclaim:

1. An overvoltage protection network comprising a voltage regulator coupled between a first terminal and a second terminal,

said first terminal including means receiving a reference voltage, v a plurality of switches each having a primary terminal coupled in common to said second terminal, each of said switches including a secondary terminal coupled to a separate utilization circuit, a first one of said switches responding to the presence of a voltage at a particular level on a respective secondary terminal to conduct and to cause the voltage regulator to operate,

said voltage regulator operating to provide a reference voltage level to prevent higher excursions of the voltage on the respective secondary terminal.

2. A network as claimed in claim 1, in which the voltage regulator includes a zener diode, and

the zener diode provides the reference voltage level when it avalanches.

3. A network as claimed in claim 1, in which the switches include switching diodes, and

the switching diodes become conductive upon the application of the voltage at a particular level to cause the voltage regulator to operate.

4. A network as claimed in claim 1, in which the voltage regulator includes a zener diode,

t eswi c sinclude switchin diodes,a d tlie switc mg diodes becom conducti ve upon the application of a voltage at a particular level,

the switching diodes, upon becoming conductive, providing a path over which the zener diode may conduct and thereby establish the reference voltage.

5. A network as claimed in claim 1, in which the network forms part of a telephone switching system,

the voltage at a particular level is provided by a test unit for testing purposes, and

means are provided for detecting the voltage at the secondary terminal to provide a pulse count.

6. A network, as claimed in claim 1, forming part of a telephone switching system, in which a plurality of sleeve leads are provided,

each of the secondary terminals is coupled to a 

1. An overvoltage protection network comprising a voltage regulator coupled between a first terminal and a second terminal, said first terminal including means receiving a reference voltage, a plurality of switches each having a primary terminal coupled in common to said second terminal, each of said switches including a secondary terminal coupled to a separate utilization circuit, a first one of said switches responding to the presence of a voltage at a particular level on a respective secondary terminal to conduct and to cause the voltage regulator to operate, said voltage regulator operating to provide a reference voltage level to prevent higher excursions of the voltage on the respective secondary terminal.
 2. A network as claimed in claim 1, in which the voltage regulator includes a zener diode, and the zener diode provides the reference voltage level when it avalanches.
 3. A network as claimed in claim 1, in which the switches include switching diodes, and the switching diodes become conductive upon the application of the voltage at a particular level to cause the voltage regulator to operate.
 4. A network as claimed in claim 1, in which the voltage regulator includes a zener diode, the switches include switching diodes, and the switching diodes become conductive upon the application of a voltage at a particular level, the switching diodes, upon becoming conductive, providing a path over which the zener diode may conduct and thereby establish the reference voltage.
 5. A network as claimed in claim 1, in which the network forms part of a telephone switching system, the voltage at a particular level is provided by a test unit for testing purposes, and means are provided for detecting the voltage at the secondary terminal to provide a pulse count.
 6. A network, as claimed in claim 1, forming part of a telephone switching system, in which a plurality of sleeve leads are provided, each of the secondary terminals is coupled to a separate sleeve lead, a test unit is coupled to a third terminal forming part of each sleeve lead, said tesT unit providing a pulse over said third terminal to activate a counter coupled to a separate sleeve lead, and a resistor connected in each sleeve lead between said respective secondary and third terminals to provide a voltage drop in said pulse as it appears at said secondary terminal, whereby the pulse is of sufficient magnitude to activate the counter, but is reduced at the respective secondary terminal. 